1. Field of the Invention
The present invention relates to an encapsulant material having enhanced light reflectivity, to a crystalline silicon photovoltaic module and to a thin film photovoltaic module.
2. Description of Related Art
A structure of a photovoltaic module includes a frontsheet, solar cells and a backsheet formed in a laminated sandwiched structure. An encapsulant material therein is mainly used as a barrier layer to protect the solar cells and connecting circuits in the photovoltaic module from environmental hazards like moisture, oxygen, acid rain and salts. A good encapsulant material not only extends life span of the module, but also maintains a certain photovoltaic conversion efficiency.
Common encapsulant materials are highly transparent thermosetting or thermoplastic polymeric materials. Since refraction coefficients (n) of the encapsulant materials are similar to that of glass, it is uncommon to directly use the encapsulant materials to enhance light trapping of the photovoltaic module. A most common example is using periodical V-groove structures disposed between the frontsheet and the backsheet of the photovoltaic module and in the interspace between the solar cells to enhance light reflectivity of a crystalline silicon photovoltaic module.
As shown in a patent layout strategic analysis of the photovoltaic modules, most patents focus on development of materials and processing technologies of the modules, and each of the companies emphasizes on highly transparent optical elements: for example solar cells with anti-reflection layer, glass substrate with texturing on its surface; another emphasis is on highly reflective backsheet, and few patents focus on structural designs of light trapping of encapsulant material of the module, thereby effectively confining sunlight in the structure of the photovoltaic module.
Relating to structural designs of high transparency optical elements and backsheets, in U.S. Pat. No. 5,994,641, the V-groove textured sheet that exposes to sunlight are disposed in the gaps between solar cell arrays, thereby being fabricated into a highly reflective optical sheet and effectively enhances light trapping and use thereof. In comparison, the present invention uses an encapsulant material with enhanced light reflectivity to devise the light reflecting and scattering properties of gaps in an array, thereby effectively improving light trapping of the gaps between solar cells.
US Patent Publication No. 2008/0000517 A1 provides a design of a highly reflective backsheet having a structure with embossed surfaces, which guides light obliquely to produce backsheet reflectivity. In comparison, the present invention uses an encapsulant material with enhanced light reflectivity, thereby using the encapsulant material to generate a condition in which scattering angle of the reflected light is greater than a critical angle, so that the sunlight is totally reflected back from the surface of the front sheet thereby, the photoenergy is effectively trapped inside the module.
The light trapping in the thin film photovoltaic module mainly uses back electrode metallic films or white paint as back surface reflectors to enhance light absorption of the photo active layer, for example in U.S. Pat. No. 5,569,332. However, the above method is unfavorable for applications in see-through type thin film photovoltaic module.